OF ELECTEIC SIGNALS THEOUGH SUBMAEINE CABLES. 
999 
analogous means, signals can he sent without confusion at any speed which will allow the 
shortest signals used to cause a sensible variation in the received current. 
The cable was available for a few days only, the apparatus used was very imper- 
fect, the paper frequently tore, the openings in it were cut by hand one by one, the 
speed of the drawing-rollers was far from regular, the relay was difficult to adjust, 
owing to residual magnetism in the electro-magnets, and the author could give but a 
small part of each day to the experiments ; in spite of these disadvantages, the results 
obtained were so definite as to leave no doubt of the important conclusion stated 
above. 
No further experiments could be made ; but indeed no further improvement appeared 
possible, except in the mechanism for making the required contacts, and in the choice 
of signals which should give the greatest number of words with the smallest number of 
currents. Neither of these points can fitly be treated of in the present paper. 
Before proceeding to compare the results obtained with the deduction from mathe- 
matical theory, or to apply the conclusions to cables in practical use, it will be well to 
consider how far the special disposition of the cable may have affected the value of the 
experiments. 
The experiments were made through dry cables, lying in large close coils, whereas 
the cable when in use lies extended under water. It is found in practice that the insu- 
lation and charge of an iron-cased cable is little affected by submersion ; but coiling 
is generally believed to cause an additional impediment to the transmission of signals, 
and it might certainly be expected that this difference of condition would cause some 
discrepancy between the experiments described and the results of practice : but since 
the mathematical theory is framed to meet the case of a submerged and extended cable 
only, whenever the conclusions experimentally deduced are found to be in accordance 
with the deductions of theory, it is clear that the experiments and the theory mutually 
confirm one another, and that the conclusions may be safely applied to the practical 
case of an extended and submerged cable ; for it is impossible to suppose that the dry 
and coiled state of the cable, not contemplated in the theory, should nevertheless 
exactly compensate its errors, or that results due only to an accidental arrangement of 
the cable should by chance coincide with deductions from a defective hypothesis. 
When, on the other hand, the results obtained differ from those given by theory, or 
even when the theory" affords no confirmation of the experimental conclusions, we must 
forbear to extend these conclusions to the practical case of a straight cable. 
The arrival-curve obtained by experiment is similar in general appearance to that 
given by Professor Thomson in “ The Theory of the Electric Telegraph The iden- 
tity of the curve obtained from the increase -with that obtained from the fall of the 
received current, follows from equation (3.) in the same paper. The described efiects 
of using alternate currents follow from the principle of superposition, by which also 
the effects of the increased speed might be shown in diminishing the received signals. 
* Vide Proceedings of the Eoyal Society, May 1855, and Philosopliical Magazine, S. 4. vol. xi. p. 146. 
